1. Field of the Invention
This invention relates to an image-taking apparatus, and more particularly to an image-taking apparatus having a filter in contact with a lens system.
2. Description of the Related Art
There has been known an image-taking apparatus which images weak fluorescence emitted from a sample in a dark box. A plurality of filters different in transmission properties are prepared for the taking lens employed in such an image-taking apparatus and one of the filters is mounted on the taking lens according to the kind of the sample to be photographed.
There has been a demand for automatically mounting a filter on the taking lens and an electric filter changing system has been investigated. In order to bring a filter in close contact with a taking lens by electric control, change of the total length of the taking lens caused by focusing must be taken into account. That is, when the filter to be positioned in front of the taking lens is held away from the taking lens due to focusing, the filter can obstruct the field of view of the taking lens, or light traveling through the gap between the taking lens and the filter can cause noise. Accordingly, the filter changing system must be provided with a function to move the selected filter following extension and contraction of the taking lens with the filter held in close contact with the front end of the taking lens.
However, in order to move the filter following extension and contraction of the taking lens with the filter held in close contact with the front end of the taking lens, control to move the filter in the direction of the optical axis of the taking lens while detecting the position of the front end of the taking lens is necessary, and especially when one of a plurality of taking lenses is selected as the taking lens, the difference in the total length of the taking lens more complicates the control, which results in high cost.